Control for rolling means having successine rolling stands

ABSTRACT

This invention is concerned with the automatic rolling of stock other than strip, plate, sheet and the like. The rolling is carried out in at least two passes and the rolling operation is controlled by adjusting at least one of the following four parameters: roll speed and screwdown of the first of the passes; roll speed and screwdown of the second of the passes, in response to at least one of: direct stock measurement; direct mill measurement; indirect stock measurement; indirect mill measurement.

United States atent Skelton et a1.

[ 1 Mar. 21, 1972 CONTROL FoR ROLLING MEANS HAVING SUCCESSIVE RQLIANGSTANDS Inventors: Charles Roger Skelton, Dronfield, Sheffield; DalipTarachand Malkani, Chesterfield, both of England Assignee: The BritishIron and Steel Research Association Filed: June 12, 1969 Appl. No.:832,571

Foreign Application Priority Data June 14, 1968 Great Britain..28,562/68 U.S. Cl ..72/8, 72/9, 72/16, 72/19 Int. Cl. ..B2lb 37/02,B21b 37/08 Field of Search ..72/8-12, 16, 19, 72/21 [56] ReferencesCited UNITED STATES PATENTS 3,222,900 12/1965 Helsing ..72/234 X3,251,207 5/1966 Wilson ..72/12 3,526,113 9/1970 McNaugher ..72/83,049,036 8/1962 Wallace et al. ...72/9 3,212,310 10/1965 Brys ..72/123,468,145 9/1969 Yeomansm. 72/l2 3,531,961 10/1970 Dunn ..72/8

Primary ExaminerMilton S. Mehr Att0rney-Bacon & Thomas [57] ABSTRACTThis invention is concerned with the automatic rolling of stock otherthan strip, plate, sheet and the like. The rolling is carried out in atleast two passes and the rolling operation is controlled by adjusting atleast one of the following four parameters: roll speed and screwdown ofthe first of the passes; roll speed and screwdown of the second of thepasses, in response to at least one of: direct stock measurement; directmill measurement; indirect stock measurement; indirect mill measure- 12Claims, 14 Drawing Figures C221 26 cm ROD/14575? fwd/73 PATENTEUMARZII972 3,650,135

snmaure SMND 7(21) STAND 2 (22) HR [Q WIDTH ERROR 24 STAND I (2!) STAND2/22) l8 I8 12 F --12 Flo. Z4.

INVENTORS CHARLES Roe-ER SKELTON DAL/P THAHC/IAND Mnum/w d w ATTORNEYSPm-mnmza I972 3,650,135

SHEET 6 [IF 6 A STAND 1(21) 23 STAND 2(22) RH U 2 2 5Q QQ 64" L F/GBA.

STAND H21) 23 STAND 2(22) FIR Q \L L. F: HSMND M21) 23 TAND 2(22) i IF/a8 INVENTORS gm ATTORNEYS CONTROL FOR ROLLING MEANS HAVING SUCCESSINEROLLING STANDS This invention relates to the rolling of relatively thickmetal stock. Such stock may be material in bloom billet, rod, bar orlike form which generally has thickness of the same order as width andthe invention is concerned with the problem of rolling of such stock toa desired cross section. Such stock is to be distinguished from stock inthe form of strip, plate and sheet the thickness of which is relativelysmall and of an order of magnitude lower than the width.

A specific solution to this problem has been given in our British Pat.No. 1,150,073 (British Pat. application No. 25,437/65). The presentapplication proposes a general solution and a number of rolling schemeswhich can be derived from the general solution.

According to the present invention in one aspect, there is provided amethod of rolling stock other than stock having, in a cross sectiontransverse the length of the stock, one dimension which is smallcompared with, and of an order of mag nitude lower than, anotherdimension normal to said one dimension, said method involving subjectingthe stock to at least two passes for producing stock on the dischargeside of the last of the two passes having a cross section substantiallythe same as a desired cross section, the method comprising controllingthe rolling operation to produce said desired cross section stock byadjusting at least one of the following parameters: roll speed of thepenultimate of the two passes; screwdown of the penultimate of the twopasses; roll speed of the last of the two passes; screwdown of the lastof the two passes; in response to at least one of: direct stockmeasurement; direct mill measurement; indirect stock measurement;indirect mill measurement.

According to the present invention in another aspect, there is provideda rolling mill for rolling stock other than stock having, in a crosssection transverse the length of the stock, one dimension which is smallcompared with, and of an order of magnitude lower than, anotherdimension normal to said one dimension, said mill comprising meansproviding at least two passes for producing stock on the discharge sideof the last of the two passes having a cross section substantially thesame as a desired cross section, and means for adjusting at least one ofthe following parameters: roll speed of the penultimate of the twopasses; screwdown of the penultimate of the two passes; roll speed ofthe last of the two passes; screwdown of the last of the two passes, inresponse to at least one of: direct stock measurement; direct millmeasurement; indirect stock measurement; indirect mill measurement tothereby control the rolling operation to produce said desired crosssection stock.

The present invention will be more readily understood from the followingderivation of the said general solution and of the followingdescription, given by way of example only, of a number of rollingschemes which can be derived therefrom. In the description, referencewill be made to FIGS. 1 to 3 which illustrate various rolling schemes.

Where the term constant roll gap system or constant gap system is usedherein this term refers to a system like that described in our BritishPat. No. 692,267.

Both the solution in the said British Pat. No. 1,150,073 and thesolution of the present application require the stock to pass throughmeans providing two rolling mill passes. The passes may be provided bysuccessive rolling mill stands, alternatively, a reversing mill mayprovide the passes. The second of the two passes may be the last pass ofa sequence or, alternatively, it may be followed by a further pass, orpasses.

The solution in the said British Pat. No. 1,150,073 requires that thescrew setting of the first pass is controlled in response to measuredstock error and that the roll gap of the second pass is fixed, ormaintained at a substantially fixed value by automatic gauge control.This solution requires there to be zero, or constant, tension in thestock between the two passes.

1n the general solution of the present application, account can be takenof tension in the stock between the two passes (in the case of thepasses being provided by successive stands) and such tension does nothave to be zero, or constant. Alternatively, in certain cases, it ispossible to properly control the rolling operation ignoring theinterstand tension.

To arrive at the general solution of the present application, equationsare established relating the input and output variables when rollingsimultaneously in two stands of a rolling mill with interstand tension.The coefficients of the equations are established by experiment. Thenotation is as follows:

H Stock height.

W= Stock width.

6 Stock temperature.

S No load roll gap setting.

N Light load roll speed setting.

(I Roll speed under load.

P= Roll separating force.

T= lnterstand tension.

V= Stock velocity.

R A reference signal used to set the required roll gap in a mill standincorporating a constant roll gap control system as described herein.

q Selected proportion of a signal from a position transducer fitted on amill stand incorporating a constant roll gap control system.

r Selected proportion of a signal from a pressure transducer fitted on amill stand incorporating a constant roll gap control system.

X Closed length of hydraulic jack.

1: Extension of hydraulic jack.

Y= Roll gap with no load on the mill stand and the hydraulic jack in itsfull closed position (i.e., with x=0).

Z =Roll gap under load.

M Stiffness of mill stand.

a, b, c, d, e, f, g, j, k, l, u, denote coefficients.

Where both upper and lower case symbols are given, the lower case symbolsignifies a small change in the corresponding upper case symbol. Thesuffix convention adopted is such that if a symbol has one suffix thenthat suffix refers to the stand number. If a symbol has two suffixesthen the first suffix refers to the stand, while the second denoteswhether the quantity occurs before the stand (0) or after it (1 Thissuffix convention does not apply to the symbols denoting co-efficients.

When rolling simultaneously in two stands of a rolling mill withinterstand tension, the following linear equations with u 8 l0 B 10 8 l31 8 2 fl3 1 g8 2 Similar relationships may be drawn up for any of theother output variables such as rolling load and torque.

If it is necessary to evaluate the co-efficients in the above equationsthey may be determined by experiment for particular steady statestandard conditions and for a particular mill and rolling condition.

As an example, the co-efficients can be calculated for rollingconditions in which a round rod is rolled in an oval pass and then in asecond, round, pass, the rolling being alternately horizontal-vertical,(i.e., the axes of the rolls on stand 2 at to those on the first stand).Experiments are first conducted to establish the steady state standardconditions. Then small perturbations, each in turn, are made in H W 6,,S S N, and N and the effects of these perturbations on H W 0,, .0 V andT are measured in each case; it will be apparent that the co-efiicientsin equations (i) to (viii) can then be evaluated. Similarly, the effectson any other output variables may be measured if required. It must beemphasized that the results so obtained apply to the particular mill andthe particular initial steady state rolling conditions for which theyare obtained.

vii.

viii.

Using equations (i), (ii) and (vi) above with the calculated values ofthe co-efficients inserted into them, it is possible for variouscombinations of the four controls to calculate the necessary changes s3,, n, and n, which.must be made in order to compensate for changes inthe input variables. Equation (vi) is used as a means of indicatingwhich combinations produce acceptable tension changes if two controlsonly are used, and with three controls supplies the third necessaryequation to solve for three unknowns if reasonable values of t areassumed.

A check on the reliability'of the equations can be made by rollingoversize input stock such that the ingoing height and width errors areboth, for example +5 percent above steady state values. Equations (i)and (ii), with the known values for the co-efficients a, b, c, d, etc.,can be used to predict the necessary screw changes on stands 1 and 2 inorder to eliminate the effects of the input errors and produce out-goingstock with the same dimensions as the steady state standard.

During actual experiments, it was found that the predicted changes inthe two screw settings were successful in eliminating the effects of theinput errors on the output dimensions and did not lead to any excessivechanges in the tension level.

For this reason a control system which controls errors by means of gapadjustments in the two mill stands without any control of tension hasbeen found to perform satisfactorily.

Reference is made herein to out-going or output stock height and width;this is to be understood as being a reference to the stock height andwidth on the output side of the second stand, or pass.

Equations (i) AND (ii) may be written as:

Where X and Y represent input variations:

It will be realized that, in theory, the two output dimensions, 11,, andW can only be controlled simultaneously by making simultaneous changesto at least two of the mill settings e.g., two screws, one screw andspeed or two speeds.

By way of example two general modes of control are discussed in detailbelow.

a. Control by Two Screws If the speed settings are not to be altered andcontrol is effected by varying s and s,, then n, =n =0 at all times.

Equations (ix) and (x) may be written as:

From equations (xiii) and (xiv) the input variables X and l during anyparticular steady state are given by:

Where s, and s are the existing screw setting variations of theparticular steady state from the standard steady state.

Under these input conditions, the desired values of s, and s: which willgive zero values of h and w may be predicted by solving equations (xiii)and (xiv) for h,, w 0.

Substituting for X and Yfrom equations (xv) and (xvi):

xiii.

xvii

xviii.

xix.

The right hand sides of equations (xxi) and (xxii) give the desiredchanges in the screw settings nquired to reduce It and w to zero(assuming the speed settings are maintained constant). b. Control by OneScrew and One Speed lf control is to take effect by altering stand 2screw and roll speed settings, and stand 1 screw and speed settings arenot to be altered, .r, =n, 0 at all times.

Equations (ix) and (x) may be written as: hm n, +e Sg Xxill. w =Y+ g, n,+e,s, ulv. Equations (xxiii) and (xxiv) are identical to equations(xiii) and (xiv) excepting that g, n, and g, n; have replaced d s, andd, s,.

Therefore, by exactly the same mathematicalprocess used 5 in (a) it canbe shown that The co-efficientsj j,, k,, 1,, n 1, and u, of equations(xxi), (xxii), (xxiii) and (xxiv) are all expressible (as indicated) interms of the basic co-efficients of the control equation and cantherefore be determined by experiment in the manner in-{ dicated. Inorder to calculate the changes in screw setting on:

the two stands, or the changes in screw and roll speed setting on stand2, to reduce the errors in output stock height and .'right hand sidesof. these equations from a knowledge of the;

determined co-efficients and the measured height and width errors.

' A similar process may be used for determining similar relationships ifit is desired to use different combinations of two of the four controlparameters (roll speeds and screw settings for the two passes). Similarequations to (xxi), (x xii), (xxv) AND (xxvi) may be derived in terms ofthe stock input errors using equations (i) and (ii).

It may be desired to additionally measure variations in they interstandtension and if these variations are found to be large under same steadystates to use them to alter a third mill setting e.g., n for the firstexample given over leaf and s for the second. In this case, each ofequations (xxi), (xxii), (xxv) AND (xxvi) would include an additionalterm which can be determined by use of equation (vi), in addition toequations (i) and (ii). I

Reference will now be made to FIGS. 1 to 8 in which like referencenumerals indicate like parts.

FIG. 1 shows calculating apparatus for evaluating the right hand sidesof equations (xxi) and xxii) so as to give the changes in screwdown onstands 1 and 2 necessary to reduce the output height and width errors tozero.

FIGS. 2 and 3 each show such calculating apparatus controlling twostands of a rolling mill according to the invention.

FIGS. 4 to 8 illustrate schematically rolling schemes which are atpresent believed to be particularly important embodiments of the presentinvention.

Turning to FIG. 1, output height and width errors are shown 2592s?! I9.Em ts The ile k s a s in screwdown on stands 1 and 2 necessary to reducethe output height and width errors to zero are shown emanating fromterminals 11. The values of the resistances 12, 13, 14 and 15 are chosenrelative to the values of the resistances 16 and 17 to give the valuesas calculated by experiment of the coefiicients jh h h, and h Thesummation of the products h h and k w and the summation of the productsj h and k w are achieved by means of the operational amplifiers 18 and20 respectively. FIG. 1 accordingly shows how signals representing thedesired screw setting changes to eliminate output stock errors h and Wcan be obtained in a simple manner.

The methods whereby these signals can be used to actuate the screwdownwill now be discussed with reference to FIGS. 2 and 3, where the twoscrew method of control has been applied.

These Figures show the rolling mill comprising a first stand 21 and asecond stand 22. The stock, for example rod, is indicated at 23 andtravels in the direction of the arrow A. The roll pass of stand 21 isoval in cross section and the roll pass of stand 22 is round incross-section. As shown in FIGS. 2 and 3, the axes of the rolls ofstands 21 and 22 are all horizontal. However, to achieve an alternatelyhorizontal-vertical rolling sequence, twist guides of known form andlocated between the stands 21 and 22 cause the rod 23 to be twistedthrough 90 between stands 21 and 22. As an alternative arrangement, toproduce an alternately horizontal-vertical rolling sequence, the rollaxes of the stand 21 may be horizontal and the roll axes of the stand 22vertical.

In each of FIGS. 2 and 3, the control system which is shown controllingstand 21 will be duplicated for stand 22 but with the use ofcoefficientsj and k so that the screwdown of both these stands will beadjusted in accordance with the measured output height and width errors.

FIG. 2 shows one method of using the signals as computed in FIG. 1 toactuate the desired screw changes on stands 21 and 22. Errors in outputstock height and width are measured by a rod, or bar, meter showngenerally at 24 and having channels 25 and 26. The signal carried bychannel 25 will represent the output height error and the signal carriedby channel 26 will represent the output width error. The signals carriedby channels 25 and 26 will be processed by a circuit which has alreadybeen described in relation to FIG. 1 which circuit will emit an errorsignal representing the right hand side of equation (xxi). This signalrepresents the desired change in screw setting for stand 1 and may betermed the screw setting error signal. This signal is fed to anamplifier 27 and from thence to servo-valve 28. The servo-valve 28 isfed by a pump 36 and is connected to a drain 31. The servo-valve 28operates a jack 32 which is used to adjust the screwdown of the rolls ofthe stand 21. The jack position is representative of the screw settingand with the arrangement shown in FIG. 2 the jack velocity wouldapproximately be proportional to the screw setting error signal. Thejack would stop in a new position only when the error signal was zero.The disadvantage with this method is that the jack position iscontrolled solely by computations made from the rod meter readings andrapid changes in load would cause errors in jack position, which wouldnot be detected until the stock reached the rod meter. In the case ofstand 21, this could represent a fairly large time interval and alsobecause of this transport lag, the rate of correction cannot be veryfast without causing instability. With this method there is also theproblem of maintaining the correct gap when no rod is being rolled. Theabove two disadvantages may be eliminated by the arrangement shown inFIG. 3. As between FIGS. 2 and 3, like parts have been given the samereference numerals.

The arrangement shown in FIG. 3 may be best understood if the operationof the constant gap control system shown within the dotted lines 37, isdescribed first. This system is shown applied to stand 1 and with noexternal inputs into the system at terminal 49, the system will operateto maintain a constant roll gap under load, i.e., the system makesadjustments in the mill setting to compensate for the elastic deflectionof the various components of the mill stand 21. Although the embodimentshown in this diagram uses a hydraulic jack 32 and a servovalve 23 toactuate movement of the rolling mill chucks, screws and wedges actuatedeither by electric motors or hydraulically may also be used for thispurpose. A positive reference signal R at 38 is used to select therequired constant roll gap.

The signal from the position transducer 51 indicates the extension x orthe change in X which is the closed length of the jack. The sense ofthis signal is negative, i.e., as the jack extends the positiontransducer 51 gives a negative signal whose magnitude is proportional tothe extension of the jack. Any proportion q of this signal can be fedinto the resistor 42 by suitable adjustment of the potentiometer 40. Thepressure transducer 50 indicates the jack pressure (which isproportional to rolling load) and provides a positive signalproportional to the magnitude of the rolling load P. Any proportion r ofthis signal can be fed into the resistor 43 by adjustment of thepotentiometer 45. The operational amplifier 46 sums the signals fed into38, 43 and 42, i.e., its output is given by This error signal is fedinto the servo-valve and if the signal has a positive sense theservo-valve allows flow into the jack so that it extends it andvice-versa. The jack attains a steady position only when the above erroris zero, i.e.,

If Y is the no load roll gap of the mill stand when the jack is in itsfully closed position (i.e., with PC) at any time under rolling load I,the actual roll gap Z will be given by xxviii. where M is the stiffnessof the mill stand as a whole and the term P/M gives the elasticdeflection of the stand.

Substituting for x from xxvii) Z=Y-R/qrP/q-+-P/M xxix. if the values ofr and q are selected such that qlr=M equation (xxix) simplified isZ=YR/q xxx. It can be seen that Z, the roll gap under load isindependent of the load and is constant when reference R is constant.The reference R may be used to initially set the gap to the desiredvalue.

When the feed back signal from the pressure transducer 50 is cut outfrom the system, the error fed to the valve will be given by Rqx, andthe control system endeavors to maintain the jack extension at at aconstant value given by FIR/ll xxxi. This is independent of load andfrom equation (xxviii) the actual roll gap under load is given by xxxii.The term R/q is equivalent to the screw position in a conventionalconventional mill and can be used to set the no load roll gap (Y-R/q).This gap however, increases by an amount P/M when the rolling load P isapplied.

In FIG. 3 the error signal representing the desired change in screwsetting for the stand 21, is shown as being fed to a resistance 33. Thescrew setting error signal is then fed through a three term controller34, (a three term controller being a well known piece of equipment),whose output signal may contain three terms, integral, proportional andderivative with respect to the input error. This signal is thenpresented to the control system shown generally at 37 for the stand 21.In particular, this signal is added to the reference signal of the gapcontrol system 37 which operates with both its .position and pressurefeed back loops closed. The signal from the three term controller andthe signals from the position and pressure feed back loops are combinedby the operational amplifier 46 having resistance 47 in paralleltherewith and the resultant signal is passed to amplifier 48; theresultant amplified signal is fed to servo-valve 28. The servo-valve 28operates the jack 32.

In any steady state, the achieved roll gap will be equal to the set rollgap (proportional to the reference signal) plus an amount proportionalto the value of the signal from the three term controller 34. The rollgap will attain a new constant value only when the screw setting erroris zero (as in the system of FIG. 2). However, if any rapid change inload occurs causing errors in jack position, the pressure and positiontransducers will detect these changes and rapid corrective action willbe taken by the inner control loops of the gap control system. Becauseof the transport lags, the rate of correction initiated by the errorsignal which is computed from rod meter readings (outer control loop)will have to be relatively slow.

Another alternative is the use of the system as described in relation toFIG. 3 but with the pressure loop of the gap control system 37 open.Here, the change in jack position will be proportional to the signalfrom the three term controller and this will reach a new steady stateposition only when the screw setting error is zero. However, the jackposition will still be maintained when sudden changes in load occurbecause of the action of the inner position loop. The existing values ofthe coefficients should be used in the equations in this alternativesystem. However, if the complete gap control system is used (with thepressure loop closed) new co-efficients will have to be determined. Itwould be possible to do this experimentally with the gap control systemin operation or by deriving the relationship between the twoanalytically.

Other methods of control are also possible. These include discontinuoussystems, self-adaptive systems and semi-predictive systems, etc.

In the discussion above, the screw corrections for the two stands havebeen predicted with the use of equations (xxi) and (xxii). In relationto the screw correction for the second stand (i.e., stand 22), however,it can be shown that only a constant roll gap control system on its ownon this stand can satisfy the system requirements. This assumes thatroll wear and expansion are neglected; this should provide the samescrew setting change as predicted by equation (xxii). It will beappreciated that the use of a constant roll gap control system on thesecond stand is the solution put forward in the said British Pat. No.1,150,073. The reasoning behind putting a constant roll gap system onthe second stand is as follows:

The changes in screw setting predicted by equations (xxi) and (xxii)must reduce both h and w,, to zero, but 11,, can only be reduced to zeroby reducing the roll gap variation from the steady state to zero, i.e.,by keeping the gap constant. In practice, however, roll wear and/orexpansion will not be negligible and a rod meter will in all probabilitybe required to measure I1 purely for resetting the reference signal tooffset errors arising out of roll wear and/or expansion.

It can be seen from the control equations that stock can be rolled tothe desired cross section by taking two stock mea' surements (H and W,,)and adjusting, in response to these measurements, 1 mill parameter(screw setting on stand 1) the roll gap on the second stand being keptconstant. In this case the only control equation in issue is equation(xxi) because the stand 2 screw setting is solely controlled by theconstant gap system. If the constant gap system on stand 2 does not overcome all errors in H then both H and W must be measured.

Instead of obtaining control by the use of equations (xxi) and (xxii)control may be obtained by the use of equations (xxv) and (xxvi). Inthis latter case, the speed and screw settings of stand 22 would bevaried to attain the control over the output height and width of therod. The screw setting change of stand 22 may be made in the same way asfor the method using two screws, namely by using a constant roll gapcontrol system on stand 22. A suitable circuit will adjust the speedsetting of stand 22 in response to measured errors in output height andwidth of the rod.

It will be seen that in the last-mentioned rolling schemes, where thesecond stand (stand 22) is controlled solely by a constant gap system,then the only control equation in issue is equation (xxi) or equation(xxv) which reduce respectively to:

because due to the constant gap control system on the second stand (or asecond stand of high stiffness) 12,, is substantially zero.

It can be seen from the foregoing control equations that a system ispossible in which the only stock parameter measured is the output width.In such a system, correction of the output width may be obtained byusing errors in output width to adjust screwdown on the first stand onlywhile stand 2 operates with a constant gap control system.Alternatively, the second stand roll gap could be kept at asubstantially constant value by using a second stand of high stiffnesswithout any form of gap control.

The errors caused by long term variations (such as roll wear) inarrangements using a constant gap control system or a stiff mill designon the second stand may be overcome by feedback of the output heighterror to stand 2 screwdown and the output width error to the screwdownor roll speed of stand 1 or the roll speed of stand 2.

When one stock dimension only is measured, that dimension must be theoutput width namely the width of the stock after leaving the secondstand, i.e., the second stand in the direction of travel of the stockthrough the two stands. This is because h is assumed to be zero. If anyother stock dimension were measured, it can be shown from the controlequations that an additional measurement (which would not be zero) wouldbe required to compute the necessary mill correction. When one dimensiononly (namely output stock width) is measured, it is preferable that therolling planes of the two stands relative to stock be mutuallyperpendicular. This can be achieved by arranging for the axes of therolls of one stand to be perpendicular to the axes of the rolls of theother stand; alternatively, the axes of the rolls of one stand may beparallel to the axes of the rolls of the other stand and the stocktwisted through between the two stands. Relative to the stock, therolling sequence may be horizontal-vertical, or vertical-horizontal,relative to the direction of travel of the stock.

It is possible to use the control equations on the basis of stockmeasurement elsewhere than after the second stand. Thus control may beeffected on the basis of stock measurements taken before the firststand, or between the two stands, or both before the first stand andbetween the two stands. However, in these cases, both stock height andwidth must be measured; also in these cases it is expected that thestock measurements will have to be used to effect adjustment in at leastone of: first stand screwdown, first stand roll speed, second standscrewdown, second stand roll speed.

In application of the invention to a reversing mill, a predictive systemmust be used. Thus height and width of the stock prior to entry into thefirst pass must be measured. These mea sured ingoing height and widtherrors may be used to predict the changes in the screwdown setting ofthe first and second passes to eliminate output height and width errors.Adjustment of the roll speed of both the passes would have little or noeffect. The prediction for the second pass may be stored. Alternatively,the roll gap of the second pass may be kept constant. After this controlaction, any height and width errors measured on the output side of thesecond pass may be used to update value of the constants used indetermining the screwdown adjustment of the first pass.

Instead of referring to stock height and width, it may be consideredmore appropriate, particularly in the case of round stock, to refer tothe rollway dimension and guideway dimension respectively. The rollwaydimension is the stock dimension measured in the direction of the rollgap and guideway dimension is the stock dimension measured perpendicularto the rollway dimension. Prior to the first stand, or pass, the rollwaydimension will be measured in the direction of the roll gap of thatstand or pass and after the second stand, or pass, the

rollway dimension will be measured in the direction of the roll gap ofthe second stand, or pass. In between the two stands, or passes, therollway dimension may be measured relative to either the first stand, orpass, or the second stand, or pass.

Measurements of stock height and width may be made either directly, forexample by means of a rod, or bar meter, or indirectly. As an example ofindirect stock measurement, the stock height measurement which insteadof being measured directly by a meter can be taken to be equal to theroll gap under load which in turn may be determined by adding the knownno load roll gap to the mill spring which in turn is a known proportionof the measured rolling load. The stock width can be obtained indirectlyby dividing the height into a measured value of mass flow of the stockfrom the second stand, or pass, or roll gap.

Also, there are means of indirect dimension error measurement that canbe drawn from equations (iii) and (iv). At any time variable changes s,,s n and n are known and it should be possible to measure stand speedchanges under load, to, and with great accuracy using good qualitytachogenerators or other suitable means.

Therefore we can write:

i io a io "2 q l 4 2 f4"1 84"2 assuming that temperature variations arenegligible. Consequently,h and w can be determined provided 11 b, 0 17.,0 which generally will be the case. Small temperature variations aboutthe chosen steady state may be assumed negligible. In a similar way, itwould also be possible to utilize equations relating load changes oneach stand with the input variables or even those that could be drawn upfor torque changes.

Thus it is possible, by use of the control equations, to measure rollspeed changes under load, or roll load changes, at one or both passesand use variations in these measurements to adjust at least one of:first pass screwdown, first pass roll speed, second pass screwdown,second pass roll speed to obtain stock on the output side of the secondpass of substantially the desired cross-section. The roll speed changesmay be measured directly, for example by means of a tachogenerator orindirectly for example by means of sound measuring apparatus which woulddetect pitch changes in the noise of the roll drive on changes of rollspeed. Roll load changes may be measured by the use of load cells.

The invention of the present application requires some method formeasuring stock height and/or width, or stock rollway and/or guidewaydimensions. For this purpose, a TV. bar meter has been developed and isthe subject of our copending application No. 700/68. It is such a meterwhich may comprise the rod, or bar, meter referred to with reference toFIGS. 2 and 3.

The following rolling schemes (see FIGS. 4 to 8) are at present believedto be particularly important embodiments of the present invention:

1 FIG. 4

Stock output width error feedback for the adjustment of stand 1screwdown with a constant gap control system on stand 2 or a stand 2 ofstiff design. No control action would be taken to alter the steady statespeed settings of the stands. This scheme can be performed by therolling mills ofFIGS. 2 and 3, it being understood that the followingmodifications would be made: (a) channel 25 carrying the output heighterror and associated circuitry would be removed so that output widtherrors only from channel 26 would be used to control stand 21 screwdownby the means disclosed; (b) stand 22 would be of stiff design or have aconstant roll gap control system applied to it in place of the stand 22control of FIGS. 2 and 3.

In FIG. 4, reference 24 is a width meter only feeding width error tothree term controller 34. Box 60 is a screwdown controller for adjustingthe screwdown on stand 1 (21) in response to the output of thecontroller 34. In the scheme of FIG. 4 and also in other schemes whereit is used, the screwdown controller 60 may comprise the screwdownadjustment mechanism of FIG. 2 or may incorporate a constant gap controlsystem and therefore comprise the screwdown adjustment mechanism of FIG.3. The jack 32 adjusts the roll screwdown of stand 1 (21) in response tothe output from controller 60. The reference 61 indicates a constant gapcontrol system for stand 2 (22) feeding jack 32; alternatively, thisstand may be of stiff design.

2 FIG. 5

Stock output width error feedback for the adjustment of stand 2 rollspeed with constant gap control on stand 2 or a stand 2 of stiff design.N0 control action would be taken to alter the steady state screwdown androll speed settings of stand 1. This scheme can be performed by therolling mills of FIGS. 2 and 3 it being understood that the followingmodifications would be made: (a) channel 25 carrying the output heighterror and associated circuitry would be removed; (b) output width errorsfrom channel 26-would be used to control stand 22 roll speed; (c) stand22 would be of stiff design or have a constant roll gap control systemapplied to it in place of the stand 22 control of FIGS. 2 and 3; (d) thecontrol of FIGS. 2 and 3 would be removed from stand 21.

In FIG. 5, the width meter 24 feeds its signal to three term controller34, the output of which feeds roll speed controller 62. In the scheme ofFIG. 4 and also in other schemes where it is used, the controller 62 maybe comprised by any one of a number of well known means for controllingmotor speed, e.g., a Ward-Lennar control system. The output ofcontroller 62 is fed to the rolls of stand 2 (22). Reference 61indicates a constant gap control system for stand 2 (22); alternatively,this stand may be of stiff design.

3 FIG. 6

Stock output wi th error feedback for the adjustment of stand 1 rollspeed with a constant gap control system on stand 2 or a stand 2 ofstiff design. No control action would be taken to alter the steady statescrewdown setting of stand 1 and roll speed setting of stand 2.

In FIG. 6, the width meter 24 feeds its signal to three term controller34, the output of which feeds roll speed controller 62 for stand 1 (21).Reference 61 indicates a constant gap control system for stand 2 (22)feeding jack 32; alternatively, this stand may be of stiff design.

4 FIGS. 7A-7E A predictive system with input stock width and heighterror (i.e., width and height error measured immediately upstream ofstand 1) fed forward (FIG. 7A) to stand I and stand 2 screwdowns (nocontrol action to alter the steady state stand 1 and stand 2 roll speedsettings), or (FIG. 7B) to stand 1 roll speed and stand 2 screwdown (nocontrol action to alter the steady state stand 1 screwdown and stand 2roll speed settings), or (FIG. 7C) to stand 2 roll speed and screwdown(no control action to alter the steady state stand ll speed andscrewdown settings), or (FIG. 7D) to stand 1 screwdown and stand 1 rollspeed (no control action to alter the steady state stand 1 roll speedand stand 1 screwdown settings), or (FIG. 7E) to stand 1 screwdown andstand 2 roll speed (no control action to alter the steady state stand 1roll speed and stand 2 screwdown). The co-efficients used may be updatedby measurement of output stock errors.

These schemes are illustrated in FIGS. 7A to 7E and it is believed thatno detailed description of these Figures is necessary bearing in mindthat the items referenced 23, 32, 34, 60, 62 have already beendescribed. In FIGS. 7A to 7E, reference 24 denotes a rod, or bar, metermeasuring both stock height and width. Line 63 carries the rollwaydimension (height) error and line 64 the guideway dimension (width)error. The boxes 65 and 66 of FIGS. 7A to 7E enclose circuits having thesame electrical components l2, l3, l6 and 18, and arranged in the samemanner, as appear in FIGS. 2 and 3. The values chosen for thesecomponents in boxes 65 and 66 are not necessarily the same as the valuesof these components in FIGS. 2 and 3 and are determined by theappropriate control equations.

5 FIGS. 8A-8C Stock output width error feedback for adjustment of stand1 screwdown or stand 1 roll speed or stand 2 roll speed together withstock output height error feedback for adjustment of stand 2 screwdownfor correction of the long term variations in the roll gap at stand 2,which embodies a constant roll gap system or is of stiff design. Nocontrol action would be taken to alter that mill parameter (steady statestand 1 screwdown and roll speed settings and steady state stand 2 rollspeed settings) not adjusted in response to the said stock measurement.

These schemes are illustrated in F IGS. 8A to SC and it is believed thatno detailed description of these Figures is necessa ry bearing in mindthat the items referenced 23, 24, 32, 34, 60, 62 have already beendescribed. Lines 63 carry the rollway dimension (height) error and lines64 the guideway dimension (width) error.

It will be realized that in the rolling schemes comprising embodimentsof the invention, the mill parameters (screwdown of each pass in thecase of rolling with a reversing mill, and screwdown and roll speed ofeach stand in the case of rolling with a multi-stand mill) will beinitially set to steady state values. Then to control the rollingoperation to eliminate output height and width errors which would ariseas a result of variations in input stock height and width, at least oneof the mill parameters is adjusted in response to stock or millmeasurement. The term stock measurement is to be construed .as coveringmeasurement of one or more stock dimensions either directly orindirectly as previously indicated. The term mill measurement is to beconstrued as covering measurement of one or more mill parameters (rollspeed or roll load) either directly or indirectly as previouslyindicated.

The following paragraphs (1) to (9) comprise a summary of the controlsystems which are intended to fall within the scope of this invention.

1. A control system for ensuring that both the output width and heightof the stock emerging from a rolling mill are kept constant. Thiscontrol is applied while rolling in at least two consecutive passeseither on a single stand if the mill is of reversing type or on twostands if the mill is a continuous type. 2. The control system of 1) mayoperate by direct measurement of outgoing width errors only in order toactuate either a screw change on the first stand or a speed change oneither of the two stands. The second stand should be of a stiff designand/or could incorporate a constant roll gap control system to providethe stand with infinite stiffness. The first stand may also be operatedto advantage by incorporating a constant roll gap control system.

3. The control system of 1) may operate by direct measurement of bothoutput height and width errors, such that height errors actuate thescrew setting of the second stand (to achieve constant roll gap at thatstand) and width errors the screw setting on the first stand or thespeed setting of either stand. A stiff second stand design would beadvantageous or alternatively the second stand could incorporate aconstant roll gap control system. A constant roll gap control system mayalso be usefully incorporated in stand 1.

4. The control system of 1) may operate by measurement of both outputheight and width errors, which when utilized in accordance withequations as devised herein, may be used to actuate stand one or standtwo speed or stand one gap setting. Stand two should be of a stiffdesign or have a constant roll gap control system.

5. The control system of (1 )may operate by measurement of both outputheight and output width errors which when utilized in accordance withthe equations as derived herein may be used to actuate stand 1 or stand2 speed or stand 1 gap setting. Stand 2 is controlled by height errorfeedback and is of stiff design or has a constant gap control system.

6. The control system of I) may operate by direct measurement both ofoutput height and width errors which when utilized in accordance withequations as derived herein may be used to actuate two or more of thefollowing four control variables, namely: the two screw and speedsettings of the stands. It may also beadvantageous to have a constantgap control system incorporated in each stand.

7. The control system of 1) may operate by direct measurement of boththe input height and width errors which when utilized in accordance withequations derived in the same manner as the equations herein may be usedto actuate two or more of the following four control variables, namelythe two screw and speed settings of the stands. It may also beadvantageous to have a constant gap control system incorporated in eachstand.

8. For the predictive case (7) above, this control system may use themeasurements of output height and width errors for the specific purposeof updating the co-efficients in the equations that enable screw orspeed setting changes to be predicted.

9. The control system of 1) may use indirect measurement of dimensionerrors by monitoring changes in mill parameters which can be related byequations derived in the same manner as the equations herein.

We claim:

1. A method of rolling stock other than stock having, in a cross sectiontransverse the length of the stock, one dimension which is smallcompared with, and of an order of magnitude lower than, anotherdimension normal to said one dimension, said method including rollingthe stock in at least two successive rolling stands with variableinterstand tension, and controlling the rolling to produce on thedischarge side of the last of the two rolling stands desired stockhaving both its height and width controlled, the control of the rollingbeing provided by simultaneously adjusting during rolling the roll gapof one of the stands and at least one other of the followingindependently adjustable parameters (i) roll speed of the penultimaterolling stand, (ii) roll gap setting of the penultimate rolling stand,(iii) roll speed of the last rolling stand, and (iv) roll gap setting ofthe last rolling stand, provided that when the last rolling stand has aconstant roll gap control system at least one of parameters (i) and(iii) is adjusted, both adjustments being made in response to errors intwo mutually perpendicular dimensions of the cross section of the stockmeasured at one location.

2. A method according to claim 1, wherein both adjustments to saidparameters are made in response to errors in cross section of thedesired stock as rolled by the last rolling stand.

3. A method according to claim 1, wherein the rolling operation iscontrolled by adjusting the roll speed of the last rolling stand inresponse to error in the width of the desired stock as rolled by thelast rolling stand, the roll gap of the last rolling stand being keptsubstantially constant.

4. A method according to claim 1, wherein the rolling operation iscontrolled by adjusting the roll speed of the penultimate rolling standin response to error in the width of the desired stock as rolled by thelast rolling stand, the roll gap of the last rolling stand being keptsubstantially constant.

5. A method according to claim 1, wherein the rolling operation iscontrolled by adjusting the roll gap setting of the penultimate and lastrolling stands.

6. A method according to claim 1, wherein the rolling operation iscontrolled by adjusting the roll gap setting of the last rolling standin response to error in height of the desired stock and another of saidparameters in response to error in width of the desired stock.

7. A rolling mill for rolling stock other than stock having, in a crosssection transverse the length of the stock, one dimension which is smallcompared with, and of an order of magnitude lower than, anotherdimension normal to said one dimension, said mill including at least twosuccessive rolling stands through which the stock is rolled withvariable interstand tension; and control means for controlling therolling to produce on the discharge side of the last of the two rollingstands desired stock having both its height and width controlled, thecontrol means being adapted to provide the control by simultaneouslyadjusting during rolling the roll gap setting of one of said stands andat least one other of the following independently adjustable parameters(i) roll speed of the penultimate rolling stand (ii) roll gap setting ofthe penultimate rolling stand, (iii) roll speed of the last rollingstand, and (iv) roll gap setting of the last rolling stand, providedthat when the last rolling stand has a constant roll gap control systemat least one of parameters (i) and (iii) is adjusted, both adjustmentsbeing made in response to errors in two mutually perpendiculardimensions of the cross section of the stock measured at one location.

8. A rolling mill according to claim 7, wherein the control means areadapted such that both adjustments to the said parameters will be madein response to errors in cross section of the desired stock as rolled bythe last stand.

9. A rolling mill according to claim 7, including a speed control foradjusting the roll speed of the last rolling stand in response to errorin the width of the desired stock as rolled by the last rolling stand,and a constant gap controller for keeping the roll gap of the lastrolling stand substantially constant.

10. A rolling mill according to claim 7 including a speed controller foradjusting the roll speed of the penultimate rolling stand in response toerror in the width of the desired stock as rolled by the last stand,controller for keeping the roll gap of the last rolling standsubstantially constant.

1 l. A rolling mill according to claim 7 including a controller foradjusting the roll gap setting of the penultimate and last rollingstands.

12. A rolling mill according to claim 7 including a controller foradjusting the roll gap setting of the last rolling stand in response toerror in height of the desired stock and a controller for adjustinganother of said parameters in response to error in the width of thedesired stock.

t l I t

1. A method of rolling stock other than stock having, in a cross section transverse the length of the stock, one dimension which is small compared with, and of an order of magnitude lower than, another dimension normal to said one dimension, said method including rolling the stock in at least two successive rolling stands with variable interstand tension, and controlling the rolling to produce on the discharge side of the last of the two rolling stands desired stock having both its height and width controlled, the control of the rolling being provided by simultaneously adjusting during rolling the roll gap of one of the stands and at least one other of the following independently adjustable parameters (i) roll speed of the penultimate rolling stand, (ii) roll gap setting of the penultimate rolling stand, (iii) roll speed of the last rolling stand, and (iv) roll gap setting of the last rolling stand, provided that when the last rolling stand has a constant roll gap control system at least one of parameters (i) and (iii) is adjusted, both adjustments being made in response to errors in two mutually perpendicular dimensions of the cross section of the stoCk measured at one location.
 2. A method according to claim 1, wherein both adjustments to said parameters are made in response to errors in cross section of the desired stock as rolled by the last rolling stand.
 3. A method according to claim 1, wherein the rolling operation is controlled by adjusting the roll speed of the last rolling stand in response to error in the width of the desired stock as rolled by the last rolling stand, the roll gap of the last rolling stand being kept substantially constant.
 4. A method according to claim 1, wherein the rolling operation is controlled by adjusting the roll speed of the penultimate rolling stand in response to error in the width of the desired stock as rolled by the last rolling stand, the roll gap of the last rolling stand being kept substantially constant.
 5. A method according to claim 1, wherein the rolling operation is controlled by adjusting the roll gap setting of the penultimate and last rolling stands.
 6. A method according to claim 1, wherein the rolling operation is controlled by adjusting the roll gap setting of the last rolling stand in response to error in height of the desired stock and another of said parameters in response to error in width of the desired stock.
 7. A rolling mill for rolling stock other than stock having, in a cross section transverse the length of the stock, one dimension which is small compared with, and of an order of magnitude lower than, another dimension normal to said one dimension, said mill including at least two successive rolling stands through which the stock is rolled with variable interstand tension; and control means for controlling the rolling to produce on the discharge side of the last of the two rolling stands desired stock having both its height and width controlled, the control means being adapted to provide the control by simultaneously adjusting during rolling the roll gap setting of one of said stands and at least one other of the following independently adjustable parameters (i) roll speed of the penultimate rolling stand (ii) roll gap setting of the penultimate rolling stand, (iii) roll speed of the last rolling stand, and (iv) roll gap setting of the last rolling stand, provided that when the last rolling stand has a constant roll gap control system at least one of parameters (i) and (iii) is adjusted, both adjustments being made in response to errors in two mutually perpendicular dimensions of the cross section of the stock measured at one location.
 8. A rolling mill according to claim 7, wherein the control means are adapted such that both adjustments to the said parameters will be made in response to errors in cross section of the desired stock as rolled by the last stand.
 9. A rolling mill according to claim 7, including a speed control for adjusting the roll speed of the last rolling stand in response to error in the width of the desired stock as rolled by the last rolling stand, and a constant gap controller for keeping the roll gap of the last rolling stand substantially constant.
 10. A rolling mill according to claim 7 including a speed controller for adjusting the roll speed of the penultimate rolling stand in response to error in the width of the desired stock as rolled by the last stand, controller for keeping the roll gap of the last rolling stand substantially constant.
 11. A rolling mill according to claim 7 including a controller for adjusting the roll gap setting of the penultimate and last rolling stands.
 12. A rolling mill according to claim 7 including a controller for adjusting the roll gap setting of the last rolling stand in response to error in height of the desired stock and a controller for adjusting another of said parameters in response to error in the width of the desired stock. 